GB1570615A - Sodium pereborate monohydrate - Google Patents

Description

PATENT SPECIFICATION ( 1 ") 1570 615

( 21) Application No 45816/76 ( 22) Filed 3 Nov 1976 ( 19) ( 31) Convention Application No 73751 ( 32) Filed 6 Nov1975 in ( 33) Luxembourg (LU) ( 44) Complete Specification published 2 July 1980 ( 51) INT CL 3 COIB 15/12 ( 52) Index at acceptance CIA 420 422 524 525 D 33 G 50 G 50 D 33 P 85 ( 54) SODIUM PERBORATE MONOHYDRATE ( 71) We, INTE Rox, a Belgian Societe Anonyme of 33 Rue du Prince Albert, B-1050 Brussels, Belgium, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the

following statement: -

The present invention relates to granular sodium perborate monohydrate, and a process for producing it.

There is a market for sodium perborate monohydrate on the one hand because of its elevated active oxygen content (theoretical value 16 03 % corresponding to the formula Na BO 3 H 20,) and on the other because it is stable up to a higher temperature than sodium perborate tetrahydrate It is thus used in special washing powders, in solid compositions for bleaching and in different particular cleaning agents.

Hitherto, the usual process for manufacturing sodium perborate monohydrate has comprised dehydrating sodium perborate tetrahydrate The literature describes various methods of dehydration and more particularly fluidised bed processes such as that described in Belgian patent 718160 filed on 17.7 68 in the name of Solvay et Cie, for example Such processes have the disadvantage of requiring two successive operations, the one leading to the manufacture of the intermediate sodium perborate tetrahydrate, the other consisting of the dehydration of the intermediate Moreover, the active oxygen losses are relatively high in view of the accumulation of the losses in the manufacture, and the dehydration of the intermediate Finally, the product obtained is porous and friable.

A one stage process for manufacturing sodium perborate with an elevated active oxygen content by reaction of a boron source (boric acid, borax or metaborates), sodium hydroxide and hydrogen peroxide in aqueous solution was the object of a US patent 2.937,998 filed on 10 10 1955 in the name of Henkel et Cie Gmb H.

This process has a number of disadvantages The technology of it is complicated.

Also, the product obtained is friable and has a very fine granulometric structure, which means that a subsequent agglomeration operation is necessary in order to obtain granules which are compatible in size with 55 those of the other constituents of washing powders.

We have now found a particularly simple process for manufacturing sodium perborate monohydrate in granular form which can 60 overcome the disadvantages mentioned above.

According to the present invention there is provided a process for manufacturing granular sodium perborate monohydrate 65 comprising the steps of fluidising a bed containing seed particles with an updraft of a fluidising gas and introducing into the fluidised bed an aqueous solution of hydrogen peroxide and an aqueous solution of 70 sodium metaborate or a mixture of the aqueous solutions, so that the fluidising gas evaporates water from the aqueous solutions, thereby enabling a deposit of sodium perborate monohydrate to be formed on the 75 seeds.

The process perfected by us proves to be particularly interesting because it enables one to obtain, in one stage, granules of sodium perborate monohydrate which flow 80 easily and have a low abrasion index, an apparant density close to that of the other constituents of washing powders and an average particle size which is compatible with that of the other constituents of the 85 said powders Advantageously, the process is also capable of producing granules having an active oxygen content which is very close to the theoretical maximum Finally, the losses in hydrogen peroxide can prove 90 to be very low in manufacture, not exceeding 5 % in weight.

The temperature of the fluid bed preferably does not exceed the temperature at which sodium perborate monohydrate begins 95 to decompose, i e about 100 C, and is generally controlled between the ambient temperature and 100 C, usually between 35 and 95 C and more preferably between 45 and 85 C The temperature of the air or 100 0 Pf 1,570,615 other fluidising gas introduced at the bottom of the fluidised bed, e g through a gauze or a distribution plate, can vary within wide limits, chiefly depending on the temperature one wishes to maintain in the bed, the amount of water to be removed and the flow rate of the fluidising gas, most often in the range of 110 to 250 WC However, other temperatures can also be employed.

The concentration of hydrogen peroxide in the aqueous solution can be varied within a wide range Advantageously the aqueous solution contains from 5 to 75 % by weight of hydrogen peroxide and preferably from 15 to 70 % by weight Lower concentrations i.e below 5 % are less preferable in economic terms because the amount of water to be evaporated is then very high On the other hand, it can be less desirable to use higher concentrations above 75 % because the solutions become more dangerous to handle.

The aqueous solution containing hydrogen peroxide can also, if required, contain certain stabilisers, e g those mentioned in the book by W C Schumb et al (Hydrogen peroxide, Reinhold Publ Corp N Y 1955).

Of these, sodium stannate and sodium phosphate are especially suitable These stabilisers are often added although they are not absolutely necessary These stabilisers are generally used at the rate of 0 001 to 1 % by weight of the weight of 100 % hydrogen peroxide Other additives can also be added to the solution of hydrogen peroxide, such as, e g perborate stabilisers, e g those mentioned by W Machu (Das Wasserstoffperoxyd und die Perverbindungen-Hydrogen peroxide and the per compounds-Vienna 1951, Springer), and more specifically, magnesium sulphate, as well as corrosion inhibitors such as the nitrates and agents to adjust the p H The perborate stabilisers can be used preferably in the range of 1 to 50 g of stabiliser per kg of 100 % hydrogen peroxide These other additives are not absolutely necessary, however.

The concentration of sodium metaborate in the aqueous solution can be varied with so a wide range, determined at the upper limit by its solubility, the upper limit being a function of the temperature of the solution, of course In practice, solutions desirably contain from 5 to 40 % by weifht of sodium metaborate, calculated as Na BO 2 Especially suitable solutions can be obtained industrially by contacting boron minerals with aqueous sodium hydroxide Such solutions usually contain from 10 to 35 % by weight of sodium metaborate, calculated as Na BO 2.

When the two solutions are introduced ipto the fluid bed by the same iniector, an additive which permits the avoidance of premature crystallisation of the perborate in the injector can be present, if desired, either in the solution containing the hydrogen peroxide, or in the solution containing the sodium metaborate, or in both A preferred additive for this purpose is sodium hexametaphosphate 70 The molar ratio of hydrogen peroxide:

sodium metaborate, introduced into the fluid bed is generally about 1: 1 Preferably there is a very slight excess of hydrogen peroxide.

Usually this ratio is in the range of 1: 1 to 75 1.12: 1, more preferably from 1 001:1 to 1.10: 1 and especially between 1 001: 1 and 1.05: 1 A higher ratio of hydrogen peroxide to sodium metaborate is less desirable because the additional hydrogen peroxide is 80 carried off by the fluidisation gas, and a lower ratio less desirable because reaction with the sodium metaborate is incomplete.

Suitably the solutions containing the reagents can be introduced into the fluidised 85 bed at the same time, either separately, by means of two separate injectors or else using a single injector, the premixture taking place inside or in the inlet to the injector These solutions can be introduced right into the 90 centre of the fluidised bed by any well known method Pneumatic injectors such as atomisers are particularly suitable for this purpose.

The temperature of the solutions can be 95 varied within quite broad limits, preferably not exceeeding that of the fluidised bed so that premature crystallisation in the injectors is avoided when concentrated solutions are being used Temperatures between the am 100 bient temperature and 70 C, preferably between 25 and 50 C, are generally used The temperatures of the two solutions can be the same or different.

In operation of the fluidised bed, seeds, 105 i.e granules of a material compatible with sodium perborate monohydrate and having dimensions smaller than those of the granules of sodium perborate monohydrate which one desires to obtain, are introduced into 110 the bed Preferably, these seeds are particles of sodium perborate monohydrate or other inorganic persalts, such as sodium percarbonate, sodium perborate tetrahydrate or perhydrated phosphates, which also ensure 115 a homogeneous distribution of the active oxygen in the product granules.

During operation, the presence in the fluid bed of seeds is essential Conveniently these seeds, at least in part, can be composed of 120 sodium perborate monohydrate fines produced during normal operation of the bed.

The proportion of seeds can also be increased by voluntarily introducing some externally produced sodium perborate mono 125 hydrate fines into the bed or by mechanically destroying, in the middle of the bed itself, a part of the granules already formed, or again by using both these processes at the same time 130 1,570,615 Sodium perborate monohydrate fines which are introduced into the bed can be obtained by one or more or all simultaneously of the following processes, namely externally grinding normal product granules, externally grinding oversize particles of the monuhydrate produced in the dryer, recovery of fines that have been carried out of the bed by the fluidisation gas or by manufacture using a separate process.

It is also possible to equip the dryer in the fluidised bed with one or more devices such as grinders, agitators or scrapers which mechanically destroy the agglomerates and promote the formation of seeds at the same time These devices also enable one to prevent conglomeration and agglomeration of particles in the bed The devices are however hardly ever used in large sized fluid beds because agglomerates normally do not form in them When it is desired to increase the proportion of seeds in the bed, we prefer to introduce crushed reject particles of sodium perborate monohydrate, or, more preferably, the fines that have been carried out of the bed by the fluidisation gas.

The bed can be charged with solid particles by any known method, e g by means of a Venturi system The solid particles generally have an average particle diameter less than 0 4 mm, most often it is between 0 01 and 0 35 mm It is to be understood that these values are given by way of example only and that particles of different dimensions can be used.

The dimensions of the particles particularly depend on the proportion of seeds present in the bed, the size of the particles being inversely proportional to the seed content The size of the grains will thus be inversely proportional to the quantity of fine sodium perborate monohydrate introduced voluntarily into the bed and to the rate at which any mechanical grain destruction devices e g grinders, situated in the bed produce fines.

The dimensions of the particles also depend on the pressure of the gas in the injector or injectors by means of which the solutions are introduced into the bed, the size of the grains being inversely proportional to the pressure.

It is thus relatively easy to regulate the dimensions of the granules to the value desired by varying the proportion of seeds to the bed, either (a) by varying the rate of introduction of seeds or production of seeds by internal destruction of the granules or (b) by varying the pressure in the injectors or again by using these two methods at the same time.

The process according to the invention can be carried out either continuously or discontinuously The fluidised bed dryer can be of cylindrical shape, of cylindrico-conical shape, in the shape of a parallelepiped or any other shape which allows one to carry out the process.

The granules can be removed from the bed by any known device, e g by elutriation 70 via the bottom of the dryer or via a small lateral tube fitted at the base of the dryer or by overflowing out through a small lateral tube, this tube thereby determining the height of the fluidised bed 75 Preferably the gases emitted from the fluid bed are passed through a fines separator such as e g a cyclone The gases extracted can either be discharged to the atmosphere or possibly at least part can be 80 recycled to the fluid bed, after the water vapour they contain has been removed by drying or condensation.

By the use of a process according to the present invention granules of sodium per 85 borate monohydrate can be obtained having a free-flowing apparent density of from 0 40 to 1 00, preferably from 0 45 to 0 95 kg dmi-, a flowability of not more than 10 seconds, being the time for a 250 g sample 90 to flow through the mouth ( 16 mm diameter) of a short stemmed analysis funnel, and an abrasion index of 10 % or less by the method hereinafter defined.

The dimensions of the granules can be 95 varied within quite broad limits However, the process is preferably controlled to obtain granules whose granulometry is similar to that of the other components of detergent powders In general, a granulometry such 100 that at least about 80 % of the granules have a diameter between 0 1 to 1 5 mm is particularly suitable An advantageous average particle diameter is from 0 3 to 0 7 mm.

Nonetheless, by modifying the conditions of 105 the granule preparation method larger or smaller granules can be prepared whilst still maintaining the characteristics of the product as regards flowability, apparent specific gravity and abrasion index 110 Sodium perborate monohydrate obtained in a process according to the present invention can compare favourably with products obtained in the past, because it can be obtained with a better abrasion index, better 115 flowability and a very low fines content.

Moreover, the product in general is not agglomerated.

Apparatus in which the process according to the invention can be carried out will now 120 be described with reference to the accompanying drawings in Figures 1 and 2 each represent a part cross-sectional view.

The apparatus in Figure 1, comprises a vertical cylindrical fluidised bed equipped 125 with means for fluidising the solid particles in the chamber, means for introducing aqueous solutions into the bed and means for recovering solid particles from effluent fluidising gas 130 4 1,7,1 4 The cylindrical fluidised bed comprises a lower chamber or wind box 5, provided with a fluidising gas inlet comprising an air pipe 23 from a pump (not illustrated) leading to a preheater 3 having a regulator 4 and an air outlet line 2 leading to the wind box 5 The wind box 5 is divided from the upper chamber, or bed chamber 1 by a perforated plate 6 having a central orifice 15 through which the shaft of a fixed blade scraper 16 passes The bed chamber 1 is provided with a Venturi tube 13, which is fed with solid particles from a vibrating conveyor 12, and air through air pipe 14, i 5 with a tube 24 through which a grinder can be introduced into the bed chamber 1 adjacent to the fixed blade scraper 16, with an overflow tube 22, and with a tube 27 through which solid particles can be elutriated The bed chamber 1 also contains an atomiser 19 having an air feed line 20 going from a preheater 21, a hydrogen peroxide feed line 18 coming from a thermostatic storage tank 17 and a sodium metaborate solution feed line 25 coming from a thermostatic storage tank 26 Above the bed chamber 1 is an expansion chamber 7, having an increased diameter, and effluent fluiding gas outlet line 8 leading to a cyclone 9 having an air discharge ventilator line 10, and a hopper 11 in which solid particles can be gathered.

In operation, the bed chamber 1 is charged with seed particles from hopper 11, conveyed along vibrating conveyer 12, into venturi tube 13, and the particles fluidised by gas pumped through gas line 2 into the wind box 5 and thence through the perforation in plate 6 Aqueous hydrogen peroxide is fed to the atomiser 19 through feed line 18, at the temperature maintained in the thermostatic storage tank 17, and sodium metaborate through feed line 25 at the temperature maintained in the thermostatic storage tank 26 and air through feed line 20, and are thereby sprayed onto the particles in the bed chamber 1 The particles are prevented from sticking to the perforated plate 6, and thereby blocking its perforations, by the fixed blade scraper 16 rotating over the surface of the perforated plate 6.

The apparatus shown in Figure 2, and its method of operation, is identical to that shown in Figure 1, except that the bed chamber 1 is equipped with two atomisers, 19 a and 19 b, of which atomiser 19 a is fed by aqueous hydrogen peroxide feed line 18 and air line 20 a and atomiser 19 b is fed by aqueous sodium metaborate feed line 25 and air feed line 20 b.

A method used for measuring the apparent free flowing density, described herein, is similar to that described in ASTM Standards D 392-38 and B 212-48, recommended respetively for measuring the apparent density of grindable powders and metallic powders.

The apparatus used differed slightly and consisted of a trunkated conical funnel located centrally above a cylindrical bucket The funnel had a top of diameter 53 mm and a base of 21 mm which was fitted with a completely removable stopper, the perpendicular height of the funnel being 58 mm, giving an effective volume of about 60 cm 3.

The bucket had an inside diameter of 37 mm, and a depth of about 46 mm giving a volume of 50 cm 3 The base of the funnel was 65 mm above the bottom of the bucket, the stopper inserted, and the funnel filled to the brim with the product to be examined, the material being levelled off using a rectilinear blade The stopper is removed from the funnel and the material is allowed to flow out into the bucket The material in the bucket is levelled off, and weighed The apparent free flowing density of the material is then given by the ratio of the weight of the material expressed in kg to the volume of the bucket expressed in dm 3.

The abrasion index referred to in the present invention is determined by the method described in the standard ISO/TC 47/WG (secretariat-86) 167 of the British Standards Institute.

The flowability of the product was determined by measuring for a particular quantity of product to pass through the orifice of the stem of a calibrated funnel The method is somewhat similar to that described in ASTM Standard D 392-38.

The apparatus consisted of a funnel cone 100 angle 600, top interior diameter of 180 mm having a polished stainless steel clack valve and a stem of length 165 mm and inside diameter 16 mm In the test, the funnel is charged with 250 g of product and the time 105 after the clack valve has been opened is measured for the material to flow out.

The resistance to agglomeration of sodium perborate monohydrate is measured by the following agglomeration test in which a 110 250 cm 3 glass vessel, fitted with a screw top, is two thirds filled with sodium perborate monohydrate and placed in an oven at 550 C for 24 hours.

Agglomeration of the product is then 115 assessed by observation, and comparison using the following scale:

the product flows freely like dry sand 9 the product flows easily with some 120 breaks 8 to 5 partial agglomeration 4 to 1 total agglomeration Certain embodiments of the present invention will now be described more fully by 125 way of Example only, without limiting the scope of the invention The particular pieces of apparatus and working methods described below can be replaced by equivalents within 1,570,615 the general disclosure herein, as will be well Initially the dryer contained sodium perknown to the expert in this field borate monohydrate having an average dia 30 meter of 0 32 mm obtained by dehydration Examples 1 to 5 of sodium perborate tetrahydrate Ex 5 lesl top The fluidised bed was continuously fed In Examples 1 to 5 apparatus of the same with aqueous solution of hydrogen peroxide kind as that described with reference to and aqueous solution of sodium metaborate 35 Figures 1 and 2 was employed using one or two atomisers located at the In the fluidised bed dryer, the bed cham centre of the fluid bed The aqueous soluber 1 had a diameter of 152 mm for a height tion of hydrogen peroxide contained magof 915 mm above the perforated plate 6, nesium sulphate, about 5 to 10 ppm sodium and the expansion chamber 7 had a diameter stannate and comparable quantities of 40 of 305 mm for a height of 300 mm The per sodium phosphate.

forated plate 6 was made from a sheet of The granulometry is regulated by the stainless steel perforated with holes of 0 5 introduction into the reactor of fines coming mm diameter, and was pierced in the centre from the cyclone, from the cyclone, from by a hole of 20 mm diameter through which the grinding of 1 mm sieve rejects of pro 45 the shaft of blade scraper 16 passed through duction and from production which passed in Examples 1 to-3 and 5, or else through through a 0 125 mm sieve In Examples 3, which was the product removed by elutria 4 and 5, a grinder, introduced through tube tion in Example 4 The scraper 16 revolved 24, was present in the bed and operated for at a speed of 50 revs per minute The 4 seconds in every 60 Operating conditions 50 granules were removed by elutriation through are summarised in Table I below, in which a lateral tube situated at the foot of the bed the yield was calculated on the basis of the mm above the perforated plate 6 in total amount of Na BO 2 added, taking into Example 5, or by flowing out through over account the stabiliser present in the finished flow tube 22, situated 400 mm in Examples product 55 1 and 2 or 650 mm in Example 3 above the The characteristics of the products obperforated plate 6 tained are shown in Table III.

l,S 70,615 TABLE I:

Examples Nos 1 2 3 4 5 Fluidisation Air Temperature Normalised flow rate o C m 3/h C Bed temperature 135-140 210 68 29 68-71 75 205 175 170 31 52 55 73 77 Number of atomisers Initial bed charge Atomiser feed Normalised flow rate Temperature Pressure H 202 solution Rate of flow Temperature Concentration of H 202 Mg SO 4 7 H 20 concentration Sodium metaborate solution Rate of flow Temperature Concentration of Na BO 2 Concentration of Na(PO 3)J 10 H 1120 Mole ratio of reactants H O 02: Na BO 2 Rate of addition of Fines Normalised air flow rate to Venturi tube Air pressure Rate of production of product Yield of sodium perborate monohydrate 1 kg 2 5 m 3/h C kg e/cm 2 kg/h C % w/w % w/w kg/h o C % w/w % w/w 2 2.5 2.5 2 1 28 25 1.5 1 25 0.57 0.75 1.33 20.1 0.54 27.2 0.81 1 1 1 5 5 2.65 49 1.6 0.56 26 0.78 1.3 1 26 45 20.9 20 9 2.35 1.5 0.54 26 0.78 1.27 20.9 2.2 1.3 0.55 26 0.78 1.3 20.2 0 0 27 0 0 27 O 1.03 m 3/h kg e/cm 2 kg/h,m 2 1.05 1 07 1 02 1 05 Nothing 1 6 0 75 1 6 1 6 1 3 0 55 1 3 1 3 23 23 23 23 23 mol% 100 95 96 98 100 Comparative Examples 6 R and 7 R By way of comparison, two continuous sodium perborate monohydrate manufacturing tests were carried out by dehydrating sodium perborate tetrahydrate in a fluid bed.

The fluid bed dryer had a cylindrical section of 150 mm diameter and a height of 1500 mm The granules were removed by overflowing through an outlet situated 320 mm above the gas distribution plate which was made from a glass fibre cloth.

The bed of particles was fluidised by introducing a current of heated air through the gas distribution plate, and was fed continuously with sodium perborate tetrahydrate having an average particle diameter of 0.265 mm and an active oxygen content of 10.17 % in weight.

The operating conditions are summarized in Table II below The characteristics of tho products obtained are shown in 'lable ll.

1,570,615 1,570,615 TABLE II

Comparative Example No 6 R -7 R Fluidisation Air 1 Temperature TC 140 200 Normalised flow rate m 3/h 11 6 1 G 4 Bed temperature _C 56 62 Feed rate of Na BO 34 H 20 kg/h 1 13 2 76 Rate of production kg/h m 2 bed 38 1 93 7 Yield of product mol % 88 9 89 3 A comparison of Examples 1-5 and Examples 6 R and 7 R shows that the process according to the invention allows one to obtain a higher yield in sodium perborate monohydrate.

Examimtion of products The different products obtained in Examples 1 to 5 were compared with those obtained in Examples 6 R and 7 R and also with a commercially available sodium perborate monohydrate.

During the course of Example 2, samples B and C were taken and similarly during the course of Example 5, samples F to K were taken These different samples were obtained by modifying the amounts of fines recycled.

The abrasion index referred to in Table III was measured according to the test described in the standard ISO/TC 47/WG 11 (secretariat-86) 167 of the British Standards Institute As this test is particularly stringent, by way of comparison, another less stringent test (test 2), which was frequently used before thei ISO test was perfected, was carried out This test was as follows: Exactly 50 g were weighed out from the fraction of the sample which was retained on the base sieve B, the mesh aperture of which was the next stage down from the average particle diameter of the product.

This sample was introduced into a rotating drum together with 200 g of lead balls of 6 mm diameter The drum was rotated at rpm for 15 minutes and then its contents were transferred without loss into a sieve of 4 mm mesh aperture which was stacked about sieve A (the mesh aperture of which sieve being a quarter of that of sieve B), which itself was stacked above a collecting tank 30 seconds sieving was done to separate the lead balls from the sodium perborate monohydrate Then the sieve A and the collecting tank were placed on to a RO-TAP (Registered Trade Mark) mechanical sieving device and sieving carried out mechanically for 15 minutes The abrasion index in % is given by the proportion of material passing through sieve B, i e by the weight of material collected in the collecting tank multiplied by 2.

The active oxygen content, the apparent free flowing density, the average particle diameter, the flowability, the abrasion index and agglomeration index were measured for each of the results summarised in Table III below.

An examination of Table III reveals that the product obtained by a process according to the present invention can attain an oxygen content which is close to the theoretical content ( 1 and 5) Moreover, the abrasion index is much lower than that observed for products obtained according to other processes.

Finally, because the process is flexible, the granulometry of the product can be varied acccording to particular needs, which is not the case in processes by dehydration, in which the granulometry of the product is a function of that of the starting material, sodium perborate tetrahydrate One can thus obtain conveniently in a one step process a product which can be incorporated directly into washing powders.

is o O TABLE 1 i 1

Example No 1 2 3 4 5 6 R 7 R Commercially available Products A B C D E F G H I J K L M Product Active Oxygen Content g/kg 160 154 154 155 156 156 159 8 160 4 162 158 159 151 1 150 7 152 Density kg/dma 0 59 0 62 0 58 0 60 0 61 0 64 0 65 0 67 0 63 0,65 0 56 0 59 0 58 0 55 Average particle diparticle mm 0 975 0 475 0 610 0 650 0 640 0 675 0 630 0 635 0 720 0 730 0 690 0 255 0 245 0 320 Flowability dry 8 6 7 7 8 7 7 7 6 6 Abrasion Index ISO Test % 4 2 8 1 6 6 5 6 6 0 5 5 3 4 5 3 3 3 2 3 5 15 6 Test 2 % 2 8 2 4 1 7 1 9 2 0 2 1 1 7 1 3 1 2 1 2 1 3 12 6 5 4 Agglomeration Index 10 10 10 10 10 10 10 hC'4 o O 1,570,615 Example 8 In this Example, sodium perborate mono-

hydrate was obtained using an apparatus similar to that described with reference to Figure 1, except that the bed chamber was parallelepipedic cross section 150 mmx 300 mm and height 900 mm The bed was charged with seeds of sodium perborate monohydrate, which were fluidised by an updraught of air, at a temperature of 160 C and at the rate of 80 m 3/hour through the perforated plate, resulting in the fluidised bed having a temperature of 74 C The seed particles in the bed were sprayed continuously using a single atomiser with an aqueous solution of hydrogen peroxide ( 50 % w/w, 1 6 % w/w Mg SO 4 7 H 20, 0 66 kg/h) and an aqueous solution of sodium metaborate ( 30 % w/w, 2 0 kg/h) The mole ratio H 202/Na BOQ was 1 07 The granular product overflowed out through a tube located 600 mm above the perforated plate, and had an average particle diameter of 0 360 mm, an active oxygen content of 166 g/kg, and an apparent free flowing density of 0 86 kg/dm 3 The molar yield of sodium perborate monohydrate, based on sodium metaborate, was 100 %.

Claims (1)

1. WHAT WE CLAIM IS:-

   1 A process for the manufacture of granular sodium perborate monohydrate comprising the steps of fluidising a bed containing seed particles with an updraft of a fluidising gas and introducing into the fluidised bed an aqueous solution of hydrogen peroxide and an aqueous solution of sodium metaborate or a mixture of the aqueous solutions, so that the fluidising gas evaporates water from the aqueous solutions, thereby enabling a deposit of sodium perborate monohydrate to be formed on the seeds.

   2 A process as claimed in claim 1 wherein the temperature of the fluid bed is maintained at between the ambient temperature and 100 C.

   3 A process as claimed in claim 2, wherein the temperature of the fluid bed is maintained at between 35 and 95 C.

   4 A process as claimed in claim 3, wherein the temperature of the fluid bed is maintained at between 45 and 85 C.

   A process as claimed in any preced 55 ing claim wherein the solution of hydrogen peroxide contains from 5 to 75 % by weight of hydrogen peroxide.

   6 A process as claimed in claim 5, wherein the solution of hydrogen peroxide 60 contains from 15 to 70 % by weight of hydrogen peroxide.

   7 A process as claimed in any preceding claim wherein the solution of sodium metaborate contains from 5 to 40 % by 65 weight of sodium metaborate.

   8 A process as claimed in claim 7 wherein the solution of sodium metaborate contains from 10 to 35 % by weight of sodium metaborate 70 9 A process according to any preceding claim wherein the molar ratio of hydrogen peroxide to sodium metaborate introduced into the fluidised bed is in the range of 1: 1 to 1 12:1 75 A process according to any preceding claim wherein the seeds contain sodium perborate monohydrate.

   11 A process according to claim 10 wherein at least some of the seeds of sodium 80 perborate monohydrate are fines produced in the process.

   12 A process as claimed in claim 11 wherein at least some of the seeds are obtained by recycling fines which have been 85 carried out of the bed by the fluidising gas, or by crushing oversize particles.

   13 A process for the manufacture of sodium perborate monohydrate substantially as described herein with respect to any of 90 Examples 1 to 5 and 8.

   14 Granular sodium perborate monohydrate whenever produced by a process claimed in any preceding claim.

   Granular sodium perborate mono 95 hydrate having an apparent free flowing density of from 0 40 to 1 00 kg/dmi, a flowability as herein defined not exceeding 10 seconds and an abrasion index as herein defined not exceeding 10 %, whenever pro 100 duced by a process according to claim 1.

   A N CALDWELL, Chartered Patent Agent, Agent for the Applicants.

   Printed for Her Majesty's Stationery Office by Burgess & Son (Abingdon), Ltd -1980.

   Published at The Patent Office, 25 Southampton Buildings, London, WC 2 A l AY, from which copies may be obtained.